1. Field of Invention
This invention relates to an improved hitch for attaching a trailer to a towing vehicle, such as, an automobile or a light truck for travel over the highways at normal traffic speeds.
2. Description of the Prior Art
The present invention has been designed to reduce or eliminate some of the problems frequently found in trailer towing.
The three principle problems involved in trailer towing are commonly referred to as fishtailing, tail dragging and bumps, surges, pitching and rolling.
Fishtailing is side to side turning and swaying of the trailer. This cyclic motion frequently causes loss of control of the towing vehicle and many accidents. Fishtailing happens primarily with systems having the pivot point of the hitch located between the trailer and the towing vehicle. Fishtailing may be relieved by: (a) moving the pivot closer to the axle of the towing vehicle; (b) use of anti-sway bars for partial relief: (c) attaching the pivot to the axle between wheels for maximum control; and (d) moving the trailer load toward its axle or axles to reduce swing inertia.
Tail dragging is the weighting down of the rear of the towing vehicle by trailer tongue load. This fault usually tilts up the front of the towing vehicle changing the caster and the camber of the front wheels which causes road wandering and steering difficulties. Tail dragging may be relieved by: (a) use of equalizer bars to lift the rear of the towing vehicle and level same: (b) moving the hitch pivot closer to the rear axle of the towing vehicle to reduce tilting: (c) attaching the hitch pivot to the rear axle of the towing vehicle to take weight off the frame of the towing vehicle: and (d) moving the trailer load to the rear of the trailer to reduce tongue load.
Bumps, surges, pitching and rolling, usually resulting from road unevenness, causes the trailer and towing vehicle to work against each other as first one and then the other responds to the unevenness of the road surface and tries to adjust itself against the resistance of its partner. Bumps, surges, pitching and rolling may be relieved by: (a) isolating the forces produced by changing the connection of the hitch from the frame to the axle of the towing vehicle; (b) reducing the transmitted intensity of forces by increasing isolation between vehicles with: (1) providing a longer drawbar: (2) providing a non-rigid drawbar having: (a) vertical resilience (spring give up and down): (b) longitudinal resilience (forward and backward); (c) twist resilience (roll compensation): (d) strong, almost rigid, side-to-side horizontal strength; and (e) using surge brakes on trailer to reduce trailer breaking forces.
In non fifth wheel hitch arrangements commonly used for towing a trailer behind an automobile or light truck the hitch includes a rearwardly extending drawbar mounted on the rear end of the towing vehicle with a ball connector fastened to the rear end of the drawbar. A ball receiving socket is secured at the front end of a tongue extending forwardly from the trailer. When the ball receiving socket is secured in place over the ball, the ball and socket provide a pivot point for the hitch about which the towing vehicle can turn relative to the trailer. The pivot point of the conventional hitch just described is most commonly located between the towing vehicle and the trailer.
When the pivot point of the hitch is between the towing vehicle and a trailer, excessive swaying of the trailer relative to the towing vehicle often occurs as a result of the bow wave of wind produced by a large passing vehicle, such as a bus, or truck. As the bus, or truck, passes the towing vehicle and trailer going in the same direction, the bow wave of wind pushes first against the rear of the trailer resulting in a force being applied to the towing vehicle which causes the towing vehicle to turn toward the near side of the road. The bow wave then progresses forwardly pass the trailer wheels and changes the direction of sway to turn the towing vehicle toward the middle of the road. As the bow wave passes the rear wheels of the towing vehicle, the sway again changes direction pushing the towing vehicle toward the side of the road again.
When the passing bus or truck is traveling in the opposite direction to the direction of travel of the towing vehicle and trailer, the bow wave generated by the bus or trailer first hits the front of the towing vehicle and progresses rearwardly thereof and then passes from the front to rear of the trailer. The bow wave thereby causes sway producing forces to act on the towing vehicle and trailer in the reverse order of the sway producing forces produced by a bus or truck traveling in the same direction as the towing vehicle.
Various factors, such as vehicle size, passing speeds, system resonant frequencies, wind strength and direction, driver reactions, roadside hills and cuts, and wind shear conditions affect the sway problem. These factors often combine in such a way that the excessive sway generated can and does cause many trailer accidents every year.
One way to reduce the effect of sidewise trailer sway on a towing vehicle is to locate the pivot point at which the trailer is connected to the towing vehicle adjacent to the rear axle of the towing vehicle. This reduces the moment arm between the pivot point and the rear wheels of the towing vehicle resulting in less torque being applied to the towing vehicle by trailer sway than is the case when the pivot joint extends a substantial distance to the rear of the towing vehicle.
Patents which disclose trailer hitches which locate the pivot point between the trailer and the towing vehicle behind and adjacent to the rear axle of the towing vehicle include the following: U.S. Pat. Nos. 1,118,236, 2,255,624, 2,397,001, 2,729,470 and 2,743,118. Each of the aforesaid patents disclose special arrangements in the hitch structure for allowing limited relative movement between the trailer and towing vehicle as required to compensate for uneven road surfaces, etc. and to provide the necessary resilience to reduce the transfer of shock between vehicles.